System and method for detecting the seat occupancy in a vehicle

ABSTRACT

Disclosed is a system for detecting seat occupancy in a vehicle, comprising a microwave transmitter and several reflectors which are provided with a small area and are disposed within a vehicle seat, especially within the backrest of the vehicle seat. A greater or smaller number of reflectors are enabled if a person occupying the seat leans forward, resulting in a jump in intensity each time an additional reflector is enabled. Said jumps in intensity can be used in an advantageous manner for detecting the exact position of the person on the seat. In particular, an airbag can be prevented from deploying and the risks associated therewith can be avoided when the person leans far forward. Alternatively, receivers can he disposed within the seat instead of reflectors.

The invention relates to a system for detecting the seat occupancy in avehicle with at least one microwave transmitter and means for reflectingor receiving the microwave radiation that are arranged within a vehicleseat in which case at least one microwave transmitter and the means forreflecting or receiving are arranged in such a way that the radiationtransmitted by the microwave transmitter can at least reach the meansfor reflecting or receiving in the case of an unoccupied vehicle seatand that depending on the seat occupancy, the means for reflecting orreceiving can influence the reflected or received radiation.

The invention also relates to a method for detecting the seat occupancyin a vehicle, with the stages: Transmitting microwave radiation andreflecting or receiving the microwave radiation by using means forreflecting or receiving which are arranged within a vehicle seat inwhich case the transmitted radiation can at least reach the means forreflecting or receiving in the case of an unoccupied vehicle seat andthat depending on the seat occupancy, the means for reflecting orreceiving can influence the reflected or received radiation.

Such systems and methods are well-known. In addition to this, they inparticular serve to influence the trigger behavior of an airbagdepending on the seat occupancy.

An example of such a system and method is well-known from U.S. Pat. No.6,199,904 B1. In this case, microwaves are transmitted by a microwavetransmitter to a reflecting structure in a vehicle seat. The reflectingmicrowaves are detected by means of a microwave receiver. Because theintensity of the reflected microwaves depends on whether or not themicrowave radiation is weakened by a person occupying the seat, the seatoccupancy can be determined by the result of the evaluation. However, adisadvantage of this system and method is that airbag control is notalways based on reliable evaluations. For example, it can be possiblethat a reflection takes place from other objects instead of from thereflection objects in the seat provided for this specific purpose. As aresult, it was pretended that the seat was not occupied which couldresult in the airbag being blocked. This could have life-threateningconsequences for the passengers of the vehicle. In addition, thecalibrations required within the framework of the embodiment are verycostly which does not make this system cost-effective in any way.Moreover, all the additional evaluations have to be completed in acomputing time which would be opposed to a dynamic measurement and inthis case a measurement would then only be made in the case of a vehicleimpact. Likewise, in U.S. Pat. No. 6,199,904 B1 no special precautionsare taken to detect an out-of-position case which, for example, means aleaning forward of the person. The detection of such an out-of-positioncase would be desirable because in such situations, the deploying of anairbag should possibly be prevented.

The “detection of the seat occupancy” includes the detection of whetheror not a seat is occupied, the detection of the position in which aperson is seated on the seat and/or the detection of the build of aperson sitting on the seat.

It is the object of the invention to make available a system and amethod which eliminate the disadvantages of the prior art and which, inparticular, make possible a reliable detection of the seat position andin this case also the out-of-position case.

This object of the invention is solved by means of the features of theindependent claims.

Advantageous embodiments of said invention are specified in thedependent claims.

Therefore, the invention in this way is based on a system of categoriesin that the means for reflecting or receiving include several elementsfor reflecting or receiving so that the number of reflecting orreceiving elements depend on the seat occupancy. While several elementsare provided, a greater or smaller number of those depending on the seatoccupancy can be covered or enabled. If a person is sitting properly inthe seat, he/she will cover a greater number of elements than if he/shemoves out of the proper seat position. Likewise, a distinction can bemade between persons with different body volumes because small personscover a smaller number of elements than persons with greater bodyvolumes. In principle, reflectors or receivers can be arranged within avehicle seat to implement the system according to the invention. Thesedifferent technical possibilities are, therefore, summarized under thegeneral term: the means or elements for “reflecting or receiving”.

It is particularly useful that several elements for reflecting orreceiving are arranged among each other within the backrest of a vehicleseat and/or a headrest of a vehicle. For example, if the microwavetransmitter is located in the front area of the motor vehicle in theroof lining, then a maximum number of elements are covered in the caseof a person who is sitting properly. If a person occupying the seatleans forward, the elements arranged among each other are enabled insuccession so that the received intensity experiences an increase instages. In this way, switching thresholds from which an airbag should nolonger be deployed can, for example, be placed in a slope of the curvein stages so that the switching thresholds precisely conform to aspecific incline of the person sitting on the seat of the vehicle.

The system according to the invention is developed further in aparticular advantageous way by the fact that the means for reflecting orreceiving are non-modulated or modulated backscatter devices and that atleast one microwave receiver which can receive the radiation reflectedfrom the backscatter devices is provided. The modulation of themicrowave radiation by means of the backscatter devices brings aboutthat the reflector can be distinguished immediately from other metallicconductive objects. For example, if the microwave radiation is reflectedby the housing of a laptop on which the front passenger in a motorvehicle is working, then this does not cause the system to take anunoccupied seat as the starting basis. Therefore, an airbag would stillbe deployed in the case of an impact. Within the framework of thispublication, the terms “reflector, reflecting, etc.” are used with avery general meaning. This does not only mean reflections in theclassical sense of the word, but also for example the retransmission ofelectromagnetic radiation by means of a modulated backscatter process.

It can be assumed that the backscatter devices are modulatingbackscatter devices. The reflection can be ascribed unambiguously to abackscatter device by means of the pattern shown by the modulation.

The system according to the invention can be developed further byimplementing the backscatter devices as passive, semi-passive,semi-active or active backscatter devices. Passive backscatter devices,in particular, have a very simple structure since they in so far do notrequire an additional energy supply and they in particular makeavailable a cost-effective solution. Semi-passive backscatter devicesare operated with additional amplifiers which in turn do not consumemuch power. Compared with the passive backscatter devices they have theadvantage that a reflection can take place with a higher intensity. Onthis basis, a more reliable evaluation can be carried out. A reliableevaluation in particular would bring about an active backscatter device,i.e. a backscatter device with active electronic components. As a resultof this, the increased microwave intensities, in particular, makepossible a reliable evaluation. However, in the case of this embodimentof said invention, the load of the occupants of the vehicle is higher onthe basis of the microwave radiation than that in the case of thepassive backscatter devices.

In addition, the system can be developed further in a particularlyuseful way by the fact that the seat occupancy on the basis of thediffraction of the microwaves influences the received intensity and thatthe received intensity provides information about the seat occupancy.Because microwave radiation, unlike for example infrared radiation, mayshow clear diffraction at an object arranged in the radiation pathbecause of its wavelength, it is possible to use the changes inintensity on the basis of the diffraction effects. In this way, an emptyseat is distinguished from a seat occupied by an adult and, for example,a distinction is also made in the case of a seat occupied by a child anda child seat because in the latter case, because of the increase inheight owing to the child seat, the microwave radiation can also bediffracted towards the elements arranged within the seating area of aseat.

It can be provided in a useful manner that the stretch of way covered bythe microwave radiation between the microwave transmitter and themicrowave receiver or the means for reflecting or receiving can bedetermined by measuring the running time. Because of this the positionof the seat can be determined. As a result, further information aboutairbag control is provided.

It can be provided in an advantageous way, in particular, that from theresult of determining the stretch of way and the result of determiningthe position of a seat it can be determined whether or not the receivedradiation was transmitted by the microwave transmitter. In principle,such plausibility considerations are unnecessary if a backscatter deviceshould be used as the reflector, but can also be used in the sense of aredundancy. Of particular use are the considerations on the basis of therunning time of the microwave signals, but only if no pattern is imposedon the reflected microwave radiation, for example, by a backscatterprocess. In this case, an additional evaluation of the position of theseat can determine whether or not the reflection at a reflector can, forexample, come from within the backrest of the vehicle seat or whether ornot the reflection, for example, comes from a laptop on the lap of afront passenger.

It is advantageous that at least one microwave transmitter and onemicrowave receiver are used as at least one microwave transmitter deviceand a microwave receiver device with a transmitter antenna and areceiver antenna. In this way, the microwave radiation arrives from themicrowave transmitter device and the microwave receiver device at thereflectors and from the reflectors back to the microwave transmitterdevice and the microwave receiver device. The microwave transmitterdevice and the microwave receiver device can, for example, be locatedwithin the dashboard of the vehicle or within the roof lining. In thecase of such an arrangement of the microwave transmitter device and themicrowave receiver device, the changes in the position of persons thathave already been described can be detected in a reliable way. Likewise,the discussed differences can be determined between persons withdifferent body volumes. However, it is also possible that a child seatcan, for example, safely be transported on the seat of the frontpassenger. The largest part of the microwave radiation arrives at thereflectors without being adversely affected in any way and then againback from these reflectors to the receiver so that the deploying of anairbag can be prevented because the child seat, in general, consists ofa synthetic material and as a matter of principle, raises the child. Asfurther safety measures it is possible to attach a further reflector tothe child seat. In this way, microwave radiation is also reflected whichwould otherwise have been absorbed by the child seat or the childsitting in the child seat. In this way, a deploying of the airbag canstill be prevented in a more reliable way. If modulating backscatterdevices are used as reflectors, then the backscatter devices within thebackrest of the seat or on the child seat can modulate the signals in adifferent way so that it can be detected in an unambiguous way thatthere is a child seat on the seat of a vehicle.

It is, in particular, useful that a control unit is provided whichtriggers, blocks or enables functions in the vehicle depending on theradiation which has been received. Detection of the seat occupancy canalso be meaningful together with other functions in the vehicle and theenabling or blocking of an airbag is, however, a particularly importantachievement of said invention.

This can also, for example, be embodied in such a way that at least onemicrowave transmitter and/or at least one microwave receiver form partof an access control and start system installed within the vehicle. Inthe case of the microwave-based access control and start systems, inparticular, the antenna for covering the interior is generally found insuch a position that it can also trigger elements arranged within thevehicle seats for reflecting or receiving. As a result, because of theembodiments of this invention in which components of the access controland start system are used to detect the seat occupancy, an integratingand in this way cost-effective measure can be made available.

For reasons of comparison, it can be advantageous that the evaluation ofsignals received by the microwave receiver can be supported or carriedout by the means which are used within the framework of an accesscontrol and start system installed within the vehicle.

The system can be embodied in such a way that the radiation path runs ina straight line. If within the said context, a radiation path running ina straight line comes into question, this refers to the scattering ofthe radiation without diffraction phenomena. In this way, saidembodiments refer to the geometrical arrangement of the components.Thus, there is a direct line of sight between the transmitter, the meansfor reflecting or receiving and/or the receiver. In this way, a simplesystem is made available, in particular.

However, it can also be useful that the path of the radiation runs byalternate routes. The microwave radiation can be navigated through thevehicle by means of conductive materials fitted in the vehicle, so thata purposeful highlighting of certain zones can be carried out withoutadditional microwave transmitter devices and receiver devices beingrequired.

In a further particularly preferred embodiment of said invention it isprovided that several elements for reflecting or receiving duringspecific time intervals can be selectively activated or deactivated andthat by allocating the elements to the time intervals, the elements canbe distinguished from one another. In this way, the elements forreflecting or receiving are triggered serially so that unambiguous timeslots are allocated to each element. This, in the case of thebackscatter devices can, for example, result in the fact that they aresupplied with power in the allocated time slots and in this way canreflect the high frequency fields in a modulated way.

Within this context it is particularly useful that the backscatterdevices can be modulated with the same frequency. In this way it ispossible to structure the transmitter and receiver devices particularlyeasy in which case nevertheless on the basis of using the modulated,reflected radiation, the complete system functionality is maintained.

However, the backscatter devices can also be modulated with differentfrequencies. In this way, only on the basis of the modulation frequencyis it possible to make a differentiation between the individualreflectors. However, also when different time slots are allocated todifferent elements, a modulation at different frequencies can bemeaningful under these circumstances because in this way the systembecomes secure through redundancy.

Therefore, the invention based on a system of categories in that themeans for reflecting or receiving include several elements forreflecting or receiving so that the number of reflecting or receivingelements depend on the seat occupancy.

On the basis of the method according to the invention, the advantagesand particulars of the system according to the invention are converted.This also applies to the particularly preferred embodiments of themethod according to the invention given in greater detail below.

In addition, it is preferred that several elements for reflecting orreceiving are arranged among each other within a backrest and/or aheadrest of the vehicle seat.

The system is developed further in an advantageous way as a result ofthe fact that the reflection takes place by means of a modulatingbackscatter process and that the radiation reflected by the backscatterprocess is received.

A preferred further development of the method according to the inventionprovides that the backscatter process is implemented by means of apassive, semipassive, semiactive or an active backscatter device.

In addition, it is also preferred that the seat occupancy influences thereceived intensity on the basis of the diffraction of the microwaves andthat the received intensity provides information about the seatoccupancy.

Another preferred further development of the method according to theinvention provides that the stretch of way covered by the microwaveradiation between the microwave transmitter and the microwave receiveror the means for reflecting or receiving are determined by the runningtime measurement.

In addition, it is useful that the position of a seat is determined andthat from the result of determining the stretch of way and the result ofdetermining the position of a seat it is determined whether or not thereceived radiation was transmitted by the microwave transmitter.

Further advantages can be obtained if according to the method of theinvention provision is made for the triggering, blocking or the enablingfunctions in the vehicle depending on the radiation which has beenreceived.

In addition it is also deemed advantageous if provision is made for thetransmitting and/or receiving to take place on the basis of an accesscontrol and start system installed in the vehicle.

Likewise, it is deemed to be useful if it is provided that theevaluation of signals received by the microwave receiver can besupported or carried out by the means which are used within theframework of an access control and start system installed within thevehicle.

As a result, the method according to the invention can be proven to beadvantageous because the radiation path runs in a straight line.

Likewise, it can be advantageous that the radiation path runs byalternate routes.

In addition, it is also useful that several elements for reflecting orreceiving during specific time intervals are selectively activated ordeactivated and that by allocating the elements to the time intervals,the elements are distinguished from one another.

Within this context, it can be provided in a useful way that thebackscatter processes which occur at the different elements use the samemodulation frequency.

However, the method according to the invention can also be proven to beadvantageous by means of the fact that the backscatter processes whichoccur at the different elements use different modulation frequencies.

The invention is therefore based on the knowledge that a particularlyreliable and nevertheless simple and cost-effective seat occupancydetection can be made available while several reflectors which areprovided with a small area are arranged within a vehicle seat. Thismakes possible a distinct separation between a person leaning slightlyforward and the so-called out-of-position case; this means the case ofwhich an airbag may on no account be deployed. In the course of a personleaning forward, steep slopes are obtained over and over in theintensity curve, namely, when an additional element within a vehicleseat is reached by the microwave radiation. Of course, the opposite alsoapplies when a person leans backward and this for example means whenmoving from the out-of-position case to a proper seat position. Withinthe framework of the system according to the invention, diffractionphenomena of the microwave radiation can be used in an advantageous waywhich is sufficiently clear, for example, compared with systemsoperating with infrared radiation. The use of microwave radiation isalso advantageous for the reason that, compared with the use of otherwave forms, for example, ultrasound, laser radiation or light andinfrared radiation, a strong absorption takes place in the human body.Microwave radiation is scattered independently of the pressure,temperature, brightness and other ambient conditions. Because of thesimplicity of the evaluation, the measuring method is carried out veryquickly so that a dynamic measurement is, for example, only possible inthe case of an impact. Further preferences of the invention can bedetected by the fact that a seat occupancy can be detected at a veryhigh speed. The time for the detection can, for example, be within themillisecond range. As a result of this, airbag control can be given adynamism which for example makes it possible, after the airbag hasalready been deployed, to influence, depending on the seat occupancy orthe position/tilt of the person on the seat, the filling of the airbag,preferably by reducing the pressure.

Particularly preferred embodiments of the invention are now explained ingreater detail on the basis of the accompanying drawings.

They are as follows:

FIG. 1 a preferred embodiment of a system according to the inventionwith a person in a first seat position;

FIG. 2 the embodiment according to FIG. 1 with a person in a second seatposition;

FIG. 3 a diagram explaining the invention;

FIG. 4 a further embodiment of the system according to the inventionwith a person in a first seat position;

FIG. 5 the embodiment according to FIG. 4 with a person in a second seatposition;

FIG. 6 a vehicle seat to be used in a system according to the inventionwith the contours of the upper part of the body of two persons ofdifferent heights;

FIG. 7 a vehicle seat to be used in a system according to the inventionwith the contours of the upper part of the body of persons havingdifferent builds;

FIG. 8 the embodiment according to FIG. 4 with a seat occupied by a babyseat;

FIG. 9 the embodiment according to FIG. 1 with a seat occupied by achild seat; and

FIG. 10 top sectional view of the arrangement shown in FIG. 9.

In the following description of the preferred embodiments of the saidinvention, the same reference symbols are allocated to the same orcomparable components.

FIG. 1 shows a preferred embodiment of a system according to theinvention with a person in a first seat position. FIG. 2 shows theembodiment according to FIG. 1 with a person in a second seat position.A microwave transmitter device and a microwave receiver device 10 arearranged in the vicinity of the roof control unit 30 of a vehicle andconnected to a control unit 22. Several reflectors 12 are arrangedwithin a vehicle seat 20 which, depending on the embodiment, can bedesigned as backscatter or as simple electrically conductive foils. Theseat 20 can usually be shifted in such a way whereby it is particularlypreferred if the position of the seat 20 can be determined.

FIGS. 1 and 2 show a person 14 sitting in different positions on a seat20. In FIG. 1, the person 14 is sitting properly. In FIG. 2, the person14 is leaning forward so that there is a clearance between the upperpart of the body of the person 14 and the backrest 26 of a seat 20. Theposition in FIG. 2 can also be designated as the out-of-position case.

Microwave radiation transmitted from the microwave transmitter and themicrowave receiver device 10 can now depending on the seat positionreach a greater or a smaller number of reflectors 12 and as a resultparticularly reflectors 12 arranged in a greater or smaller number inthe backrest 26 of a seat 20. Accordingly, the intensity reflected bythe reflectors 12 and the intensity received by the microwavetransmitter device and the microwave receiver device 10 therefore dependon the seat position of the person 14.

In addition to the evaluation of the reflectors in the backrest of aseat or the headrest of a seat, it is also particularly useful toevaluate the sensors in a seating area of a seat because on this basisit is possible to detect the seat occupancy and, in particular, alsosituations which can be designated as the out-of-position case.

FIG. 3 is a diagram explaining the invention. The shown intensity curvedepending on the tilt angle of the person 14 shown in FIGS. 1 and 2results from the successive enabling of the different reflectors 12 inthe backrest of a seat 26. If the person 14, departing from the positionshown in FIG. 1, leans forward then the topmost reflector will first ofall be enabled which results in a slope in the intensity curve. If theperson 14 leans farther forward, then the relations do not change orhardly change at all. Only when the next reflector 12, i.e. the middlereflector 12, within the backrest of a seat 26 is enabled, will the nextslope in the intensity curve occur. The same happens when the bottommostreflector 12 is enabled. If the arrangement of the reflectors 12 and theswitching threshold are selected in a coordinated way for theout-of-position case, then the switching threshold can, for example, beplaced in a slope of the intensity curve as can be seen in FIG. 3. Inthis way, a tilt angle without a wide fluctuation range can be definedin which case the presence of the out-of-position case is assumed.

It is particularly useful if the different reflectors can bedistinguished from one another. This concerns both the reflectorsarranged in a vehicle seat and the reflectors which can be arranged inthe different seats of a vehicle within a vehicle or in other positionswithin the vehicle. It is particularly useful to use backscatter devicesas reflectors, said backscatter devices being activated at differenttime intervals. This activation, may for example take place by supplyinga current to the specific backscatter device while the backscatterdevice is deactivated in the currentless state. If the active timeintervals are now unambiguously allocated to the backscatter devices,then the individual backscatter devices can be detected unambiguouslyvia this allocation. Therefore, it is possible to work with narrow bandmicrowave radiation because a differentiation between the differentbackscatter devices via different modulation frequencies is notrequired. Via such a modulation with different frequencies, it ispossible to make a distinction between the backscatter devices, but alsoalternatively or in addition to making a distinction via the timeintervals.

FIG. 4 shows a further embodiment of the system according to theinvention with a person in a first seat position. FIG. 5 shows theembodiment according to FIG. 4 with a person in a second seat position.In the case of the system shown here, the reflectors 12 are onlyarranged within the backrest 26 of a seat 20 and this actually means notin the seating area which is contrary to the views according to FIGS. 1and 2. It is in many cases sufficient to detect the out-of-position caseshown in FIG. 5. As a further difference to FIGS. 1 and 2, in the caseof the systems according to FIGS. 4 and 5, the microwave transmitterdevice and the microwave receiver device 10 and the allocated controlunit 22 are arranged in the cockpit 24 of the vehicle. Also in thiscase, the reflectors 12 are enabled in succession when a person 12 leansforward. In the case of this arrangement, diffraction phenomena of themicrowaves play an important role because in the case of the viewaccording to FIG. 3, the direct line of sight between the reflectors 12and the microwave transmitter device and the microwave receiver device10 still does not exist or only exists partially. However, because ofthe diffraction effects, the microwaves nevertheless arrive from themicrowave transmitter device and the microwave receiver device 10 at thereflectors 12 and vice versa from the reflectors 12 at the microwavetransmitter device and the microwave receiver device 10.

FIG. 6 shows a vehicle seat to be used in a system according to theinvention with the contours of the upper part of the body of two personsof different heights. Here, a further example of an application is givenin the case of which the advantages of using reflectors 12 with a smallarea within a vehicle seat 20 or in particular within the backrest of avehicle seat 26 are illustrated. The reflectors 12 are arranged in theform of an array. A tall person 14 covers all the reflectors 12 arrangedin the backrest 26 of a vehicle, whereas a short person 32 for example achild, only covers the bottom reflectors 12. Therefore, by means of thissystem an unambiguous distinction can be made between tall and shortpersons especially as not only a gradual difference in the reflectedintensities will be determined, but a difference in leaps on the basisof the complete enabling of the top reflectors 12 which have small areasif a short person 32 moves on the seat.

FIG. 7 shows a vehicle seat to be used in a system according to theinvention with the contours of the upper part of the body of personshaving different builds. A person 40 with a large body volume and aperson 14 with a small body volume are shown. In the case of a suitablearrangement of the reflectors 12 within the backrest 26 of a vehicleseat 20, all the reflectors 12 can be covered by the person 40 with alarger body volume whereas the outer reflectors 12 are enabled by thethinner person 14.

FIG. 8 shows the embodiment according to FIG. 4 with a baby seatoccupying a vehicle seat. Here there is a baby in a child seat, in thiscase in a so-called reboard seat 18. This seat is fastened properly tothe passenger seat 20. On the basis of the relative positions of themicrowave transmitter device and the microwave receiver device 10, thereflectors 12 and the reboard seat 18 there is only a limitedattenuation of the microwave radiation. Therefore, a deploying of theairbag is prevented. In addition, it is possible that under certaincircumstances and even very meaningful to fasten reflectors to the backof the reboard seat 18. Therefore, for example, in the case of a specialmodulation of the microwave radiation by reflectors, because of arunning time measurement or by allocating different time slots to theindividual reflectors, the situation with a child seat 18 on the seat 22can be distinguished from the situation without an object on a seat 20.If for example in the case of the system according to the invention, thereflectors 12 are obscured by a metallic object, this results in astrong reflection. The intensity of this reflection can possibly forexample be in the same order of magnitude as the intensity of thereflection by the reflectors 12. There are now different possibilitiesfor the control unit 22 to detect the different situations. If thereflectors are backscatter devices with an unambiguous coding, whetherthrough the modulation frequency or the time slots, the reflection is onthis basis unambiguously detected by the obscuring metallic object.Alternatively or additionally, the reflection can be detected by ashadowing, metallic object on the basis of a running time measurement,particularly if the running time is compared with the actual seatposition which can be determined by an additional sensor.

Likewise, it is advantageous that objects without or with slightelectrical conductivity in front of the reflectors 12, only slightlyobscure the reflectors 12. Therefore, the signals received from thecontrol unit conform to the situation “empty seat” so that a deployingof the airbag is blocked in the correct way.

FIG. 9 shows the embodiment according to FIG. 1 with a child seatoccupying a vehicle seat. On the basis of the system according to theinvention, the situation shown here can also be distinguished from aperson leaning forward. A child 32 sits on a child seat 34 which isarranged on a seat 20. Several reflectors are arranged both in theseating area 28 of the seat 20 and in the backrest 26 of a seat 20. Onthe basis of a child seat 34 which in general absorbs the microwaves toa much lower extent than the body of a child 32, it is possible,particularly on the basis of diffraction phenomena, for microwaves tofind their path between the microwave transmitter device and themicrowave receiver device 10 and the reflectors 12 within the backrest26 or the seating area 28 of a seat. Therefore, the reflectors 12 withinthe seating area 28 receive a higher intensity than they could receiveif an adult person were sitting directly on the seating area 28 of theseat.

In this way, by means of a suitable arrangement of several reflectors 12and a corresponding suitable arrangement of the microwave transmitterdevice and the microwave receiver device 10, different situations with aview to the seat occupancy in the vehicle can be detected.

FIG. 10 is a top sectional view of the arrangement shown in FIG. 9. Theline of cut in FIG. 10 is made along the plane shown by an A in FIG. 9.Different ways are shown of how the microwave radiation can reach thereflectors 12 in the backrest of a seat 26 in which case the situationof a child 32 on a child seat 34 is taken as the starting point. On theone hand, there is the direct path 32 between the microwave transmitterdevice and the microwave receiver device 10 and the reflectors 12 whichin said situation are obscured by the child 32. Because of the clearancebetween the child 32 and the reflectors 12 which is, in each casemaintained by the child seat 34, it is however possible that microwavesfor example by diffraction around the body and by reflection orscattering also often on indirect paths 38, arrive from the microwavetransmitter device and the microwave receiver device 10 at thereflectors 12 and vice versa. This is only adversely affected negligiblyby the child seat 34 because compared with the human body it has a muchlower absorption capacity.

The principle of said invention was explained on the basis of the abovedescription of the accompanying drawings by a system whereby reflectors,i.e. particularly backscatter devices, are arranged in a vehicle seat.

In this case, a microwave transmitter and a microwave receiver arerequired. The microwave transmitter transmits microwave radiation in thedirection of the reflectors. The reflectors reflect the microwaveradiation in the direction of the microwave receiver. Preferably,microwave transmitters and microwave receivers are implemented in theform of a microwave transmitter device and a microwave receiver device.However, the invention also refers to systems in which, instead ofsmall-area receivers, small-area reflectors are arranged in a vehicleseat. In this case, a microwave transmitter which transmits microwaveradiation in the direction of the receiver arranged in the seat issufficient. Because of the tilting of a person on the seat, theadvantageous intensity curves can likewise be reached in this way,particularly while the intensities of the single receiver arranged inthe seat are summarized.

The invention can be summarized as follows. Disclosed is a system fordetecting seat occupancy in a vehicle, comprising a microwavetransmitter 10 and several reflectors 12 which are provided with a smallarea and which are arranged within a vehicle seat 20, especially withinthe backrest 26 of the vehicle seat 20. A greater or smaller number ofreflectors 12 are enabled if a person 14 occupying the seat 20 leansforward, resulting in a jump in intensity each time an additionalreflector 12 is enabled. Said jumps in intensity can be used in anadvantageous manner for detecting the exact position of the person onthe seat. In particular, an airbag can be prevented from deploying andthe risks associated therewith can be avoided when the person 14 leansfar forward (so-called out-of-position case). Alternatively, receiverscan also be arranged within the seat 20 instead of reflectors 12.

The features of the invention disclosed in said description, on thedrawings as well as in the claims, can be taken into consideration bothindividually and in any combination for implementing the invention.

1-33. (canceled)
 34. A system for detecting seat occupancy in a vehicle,comprising: at least one microwave transmitter; a plurality ofmodulating backscatter reflectors disposed in a vehicle seat of thevehicle; at least one microwave transmitter; wherein said at least onemicrowave transmitter and said reflectors are disposed and configuredsuch that: radiation transmitted by said microwave transmitter reachessaid reflectors when the vehicle seat is not occupied; radiationreflected from said reflectors is influenced in dependence on a seatoccupancy; and said backscatter reflectors are distinguishable from oneanother by a modulation pattern modulated onto the reflected radiation.35. The system according to claim 34, wherein said reflectors arearranged in at least one of a backrest of the vehicle seat and aheadrest of the vehicle seat.
 36. The system according to claim 34,wherein said backscatter reflectors are backscatter devices selectedfrom the group consisting of passive devices, semipassive devices,semiactive devices, and active devices.
 37. The system according toclaim 34, wherein: the seat occupancy influences an intensity of areceived signal due to a diffraction of microwaves; and the intensity ofthe received signal provides information about the seat occupancy. 38.The system according to claim 34, wherein said at least one microwavetransmitter and said at least one microwave receiver together form amicrowave transmitter/receiver device with a transmitter antenna and areceiver antenna.
 39. The system according to claim 34, which comprisesa control unit configured to selectively trigger, block, or enablefunctions in the vehicle depending on the reflected radiation.
 40. Thesystem according to claim 34, wherein said at least one microwavetransmitter and/or said at least one microwave receiver form a part ofan access control and start system of the vehicle.
 41. The systemaccording to claim 34, wherein the signals received by said microwavereceiver are processed for evaluation with means used in an accesscontrol and start system installed in the vehicle.
 42. The systemaccording to claim 34, wherein said microwave transmitter and saidreflectors are disposed to define a radiation path running in a straightline.
 43. The system according to claim 34, wherein said microwavetransmitter and said reflectors are disposed to define radiation pathsrunning with diversions.
 44. The system according to claim 34, whereinsaid reflectors are selectively activatable and deactivatable duringspecific time intervals, said reflectors are allocated given timeintervals, and said reflectors are distinguished by the allocated timeintervals.
 45. The system according to claim 34, wherein said pluralityof backscatter reflectors are modulated with a common frequency.
 46. Thesystem according to claim 34, wherein said plurality of backscatterreflectors are modulated with mutually different frequencies.
 47. Amethod for determining a seat occupancy in a vehicle, which comprises:transmitting microwave radiation towards a vehicle seat, and reachingthe vehicle seat with the radiation at least in case the vehicle seat isunoccupied; reflecting the microwave radiation at reflectors in the formof backscatter devices disposed in the vehicle seat, and influencing thereflected microwave radiation in dependence on the seat occupancy bymodulating the radiation by a modulating backscatter process; andreceiving the reflected microwave radiation and distinguishing thebackscatter devices from one another by a modulation pattern modulatedonto the reflected radiation.
 48. The method according to claim 47,which comprises arranging the reflectors in at least one of a backrestof the vehicle seat and a headrest of the vehicle seat.
 49. The methodaccording to claim 47, which comprises providing backscatter devicesselected from the group consisting of passive, semipassive, semiactive,and active backscatter devices.
 50. The method according to claim 47,wherein the seat occupancy influences an intensity of a received signaldue to a diffraction of microwaves; and the method comprises deducinginformation about the seat occupancy from the intensity of the receivedsignal.
 51. The method according to claim 47, which comprises furtherutilizing the received signal for triggering, blocking, or enablingfunctions in the vehicle.
 52. The method according to claim 47, whichcomprises transmitting and/or receiving with an access control and startsystem installed in the vehicle.
 53. The method according to claim 47,which comprises carrying out or supporting an evaluation of the receivedsignals within a framework of an access control and start systeminstalled in the vehicle.
 54. The method according to claim 47, whichcomprises causing the radiation to follow a straight line radiationpath.
 55. The method according to claim 47, which comprises causing theradiation to follow diversion routes.
 56. The method according to claim47, which comprises: selectively activating and deactivated thereflectors during specific time intervals; and distinguishing thereflectors from one another by a time interval respectively allocatedthereto.
 57. The method according to claim 47, which comprises utilizinga common modulation frequency for backscatter processes occurring at thedifferent reflectors.
 58. The method according to claim 47, whichcomprises utilizing mutually different modulation frequencies forbackscatter processes occurring at the different reflectors.